1. Field of the Invention
The present invention relates to an adhesive and a method of encapsulating an organic electronic device (OED) using the same.
2. Discussion of Related Art
An organic electronic device (OED) refers to a device including an organic material layer that generates an alternating current with electric charges through the combination of holes and electrons, and examples of the OED may include a photovoltaic device, a rectifier, a transmitter and an organic light emitting diode (OLED).
Among the OEDs, the OLED has low power consumption and rapid response time and is desirable in manufacturing a thin display or lighting device, compared to a conventional light source. Also, the OLED is expected to be applied to various fields such as a variety of portable devices, monitors, notebook computers and televisions due to its excellent space accessibility.
Durability is one of the most important problems to be solved in order to commercialize an OLED and expand its use. An organic material and metal electrode included in the OLED are easily oxidized by external factors such as moisture. Thus, a product including the OLED is highly sensitive to environmental factors. Accordingly, a variety of methods have been proposed to effectively prevent oxygen or moisture from penetrating into an OED such as an OLED from the external environments.
A method of processing a metal can or a glass into a cap shape having a groove and loading the groove with a powdery dehumidifying agent to absorb moisture or manufacturing a metal can or a glass in the form of a film and sealing the film using a double-sided adhesive tape has been used in the art.
Japanese Patent Laid-Open Publication No. Hei9-148066 discloses an organic EL element including a stacked body having a structure in which an organic light emitting layer made of an organic compound is arranged between a pair of facing electrodes, an airtight container configured to protect the stacked body from the air, and a drying unit such as an alkaline metal oxide or an alkaline earth metal oxide arranged in the airtight container. However, such an organic EL element has problems in that the entire thickness of a display device is increased due to a shape of the airtight container, it is vulnerable to physical impacts due to the presence of the internal space, and its heat radiation property is poor when it is manufactured on a large scale.
U.S. Pat. No. 6,226,890 discloses a method of desiccating an electronic device including a desiccant layer formed using a desiccant and a binder, wherein the desiccant includes solid particle having a particle size of 0.1 to 200 μm. However, the desiccant layer has insufficient moisture absorption capacity. When a curable resin in a cured state does not meet a water vapor transmission rate (WVTR) of 50 g/m2·day or less due to the characteristics of the binder surrounding a moisture absorbent, the curable resin does not exert sufficient performance because its moisture apposition rate actually increases during an acceleration test.
In order to solve these problems, Korean Patent Publication No. 2007-0072400 discloses an organic EL element. When an epoxy sealant includes a moisture absorbent, the epoxy sealant serves to chemically absorb moisture passed into the organic EL element and slow moisture penetration into the organic EL element. However, physical damage may be caused to the organic EL element due to volume expansion caused by reaction of the moisture absorbent with moisture. Also, when a metal oxide is used as the moisture absorbent, the metal oxide may react with moisture to generate a strongly basic substance, which causes chemical damage to a passivation layer and a cathode layer.
Therefore, there is a demand for development of an encapsulation material capable of effectively preventing penetration of moisture and also reducing damage to an OED.